Because the Jews felt they were the entire “building” YHWH was preparing, Paul had to come down heavy on them. The Jews figured they had an “in” with God and never realized that Yeshua was the fulfillment of the foundation YHWH had laid. Yes, I understand why they thought that. I mean, YHWH had called them, created, them, and even called them, “His Chosen People.” This is why Paul asks such a logical question:

Is there any advantage then in being one of the chosen people? Does circumcision mean anything? Yes, of course, a great deal in every way. You have only to think of one thing to begin with – it was the Jews to whom God’s messages were entrusted. Some of them were undoubtedly faithless, but what then? Can you imagine that their faithlessness could disturb the faithfulness of God? Of course not! Let us think of God as true, even if every living man be proved a liar. Remember the scripture? ‘That you may be justified in your words, and may overcome when you are judged’” —Romans 3:1-4

Clarence Jordan tries to make this personal for Christians:

“What’s the advantage, then of being a Christian? Or what’s the benefit of church membership? Well, there are all sorts of things. In the first place Christians are trustees of the Word of God. All right, so some of them are hypocrites; does their hypocrisy nullify God’s sincerity? Hell no. Let God remain true, even if it makes a liar out of every man. To quote the Scriptures: ‘. . . that you may prove right in all your sayings, And have the final word on your day in court.’—Romans 3:1-4 Cotton Patch Version